Elemental and isotopic analysis of americium in non-separated spent fuels using high resolution ICP-OES and sector field ICP-MS

Abstract

As there are no matrix-matched certified reference materials, accurate and straightforward analytical procedures for the determination of americium (Am) in non-separated spent fuels employing high resolution ICP-OES and sector field (SF-) ICP-MS were developed and cross-validated. One spent (Th,Pu)O₂ fuel and two U/Pu-based spent fuels representing different chemical and isotopic compositions were analysed for their Am content. Even though the lowest limit of detection (0.07 μg kg⁻¹) was obtained at λ = 283.226 nm, the ICP-OES signal at λ = 408.929 nm provided the most accurate results for the analysis of the spent fuel among the six investigated Am emission wavelengths. Massive spectral interference from Th precluded the use of the λ = 283.226 nm emission line for Am analysis of the (Th,Pu)O₂ fuel, while other potential interferences from plutonium (Pu) and neptunium (Np) could be excluded for all the tested Am wavelengths. Employing ICP-OES, both external calibration and standard addition yielded comparable Am amount concentrations. Calibration of the SF-ICP-MS response for Am was accomplished using both ²³²Th and ²³⁸U signals as well as applying the related mass bias. This calibration methodology that is frequently used in the absence of an Am stock standard solution was tested against a home-made ²⁴¹Am stock standard solution underlining the validity of this calibration approach. Sector field ICP-MS analysis essentially confirmed the Am concentrations obtained using ICP-OES in the three spent fuel solutions with mean values overlapping within their standard deviations. Considering isotopes of other actinides such as Pu and curium (Cm), the Am isotopic abundance (²⁴¹Am, ²⁴²Am, ²⁴³Am) was established in two non-separated fuel solutions comparing well with model calculations based on the ORIGEN-2 code.